ELECTROCHEMICAL THERMODYNAMICS 723 



and 



iHo (1 atm.) + AgCl ^ Ag + HCl(w2). 



By combining these cells we obtain the very important con- 

 centration cell without liquid junction, 



Ag I AgCl 1 HCIK) 1 H2 I Pt I H2 I HCl(wO 1 AgCl | Ag; 



to which will correspond the cell process 



HCIK) ->HCl(wi). 



This means that the sum of all the changes occurring in this 

 cell during the passage of the current is the transfer of hydro- 

 chloric acid from a solution at a concentration wa to one at a 

 concentration rtii. In other words, the process may be regarded 

 as the reversible removal of one mol of hydrochloric acid from 

 an infinite quantity of solution at a concentration W2, and its 

 addition to an infinite quantity of solution at a concentration 

 mi. The reversible electrical work will be ±(£"1 — E2)F. 



According to equation [104] (Gibbs, I, 89), the chemical po- 

 tentials of the components of a phase are 



(37) [104] 



ar 1 9f 1 



'"I = IIT ' ^2 = -7— , etc. 



OUi J p, «, nj, . . . Tin "'^2 Jp, t, ni, n„ ... nn 



This formula refers to the change in f for an infinitesimal 

 change of composition in a finite phase. Correspondingly we 

 have for a finite change of composition in an infinite phase 



iui=^l »M2 = ^^1 ,etc. (38), 



ZiTil Jp, t, nj, • • • n„ AW2 Jp. t, n,, nj, • • • nn 



where the operator A refers to the change in value of a function 

 or a variable in a finite process. Thus, if we add one gram of 

 component 1 to a very large quantity of the solution under 

 the conditions specified by the subscripts, mi will equal the in- 

 crease in f of the phase. If the unit of mass is the mol, ni will 

 equal the corresponding increase in total thermodynamic poten- 

 tial upon the addition of one mol. 



